Uranium-tin-zirconium corrosion resistant alloy



United States Patent M 3,147,088 URANIUM-TlN-ZIRCONIUM CORROSIONRESISTANT ALLOY Herbert S. Kalish, Jackson Heights, and Henry H.Hausner, New York, N.Y., assignors, by mesne assignments, to the UnitedStates of America as represented by the United States Atomic EnergyCommission No Drawing. Filed June 23, 1953, Ser. No. 373,462 8 Claims.(Cl. 29-194) This invention relates to a corrosion resistant alloy. Moreparticularly, it relates to a corrosion resistant alloy of zirconium,uranium and tin.

Fuel elements for nuclear reactors frequently contain uranium. They mayalso contain zirconium as a diluent. In some reactors, for example,alloys of uranium and zirconium are considered useful for this purpose.The extent of dilution of the fuel with zirconium in these cases is amatter of choice and depends on the power level at which the reactor isto be operated. One of the undesirable characteristics of these alloysis, however, its susceptibility to corrosion particularly at theelevated temperatures which prevail in the reactor. Since these alloysconstitute the core of the fuel element and since the core is frequentlyclad in a corrosion resistant material, such as zirconium, the corrosionresistance might not be considered to be much of a problem. However,this is not entirely true for under optimum conditions it would bedesirable to have a core which is entirely corrosion resistant or whichat least can withstand a degree of corrosion in those cases in whichthere might be a break or leak in the cladding material.

An object of this invention is to improve the corrosion resistance ofthe zirconium uranium alloys.

A further object of this invention is to provide a zirconium uraniumfuel element for nuclear reactors which can withstand the corrosiveaction of water at elevated temperatures.

It is a further object of this invention to provide a fuel element ofzirconium uranium alloy which need not be provided with a corrosionresistant cladding material.

It has been found that these objects and other advantages incidentalthereto can be obtained by incorporating in the zirconium uranium alloya small percentage of tin.

Alloys of this type are readily made by powder metallurgical techniquesin which the zirconium powder, uranium powder and tin powder arehomogeneously mixed in the desired proportions and then pressed andsintered. It has, however, been found that a good corrosion re- "trtantalloy can only be obtained in those cases in which the uranium and tincontents are kept below a certain maximum limit. In the case of uraniumthis limit is approximately 30% whereas in the case of tin the limit isin the neighborhood of 10%, with the balance of the alloy beingzirconium. In those cases in which the percentage of uranium in thealloy exceeds 30%, the tin content is no longer effective in retardingthe corrosion of the uranium zirconium alloy and, although experimentshave indicated that alloys containing more than 10% of tin are betterthan alloys which contain no tin at all, they are not as good as thosealloys in which the percentage of tin lies within the range of 1 toAlloys of this type can be prepared in somewhat the following manner.The starting materials are preferably 325 mesh zirconium hydride orzirconium, 325 mesh uranium and -325 mesh tin. In the following specificexamples the zirconium hydride is used; however, zirconium powder issometimes preferable. 11.88 parts of zirconium hydride, .63 part ofuranium and .25 part by 3,147,088 Patented Sept. 1, 1964 weight of tinmaking a total of 12.76 parts are preferably tumbled in an inertatmosphere such as, for example, argon for a period of about two hours.The mixture can then be pressed at a pressure of about 50 tons persquare inch in a die and then sintered for about 10 hours atapproximately 1320" C. which operation is preferably carried out in avacuum furnace. At the end of this treatment a material should beobtained which has an approximate density of 6.76 grams per cubiccentimeter and having a Rockwell A hardness of about 65. Materialsprepared in this manner were subjected to a corrosion test by placingthe samples in water at 315 C. and then weighing the samples at regularintervals to determine the gain in weight due to oxidation. In makingthese tests care must be taken since occasionally there may be a loss inweight owing to powdering and falling away of powder. When such testswere carried out and the corrosion rate expressed in milligrams gainedor lost per square centimeter of surface exposed per month, thefollowing results were obtained. An alloy consisting of 1% uranium byweight, 0% tin gained 7.44 milligrams per month per square centimeter ina two week test period and had a white powdery coat. By comparison analloy containing 1% uranium and 2% tin and the balance of 97% zirconiumhad a corrosion rate of only .08 in the same period. Similar resultswere obtained when the tin percentage was increased to 3 and 5%. Instill other tests which were run with alloys containing 2% uranium, 98%zirconium and no percent of tin, the corrosion rate was found to beabout 6.38 in the same period, and the sample exhibited a black andWhite color and a powdery coat. By comparison a composition of 2%uranium, 1% tin and 97% zirconium showed a corrosion rate of only .16milligram per square centimeter per month when tested for the sameperiod.

Results, such as expressed above, strikingly show the inhibition ofcorrosion caused by the addition of a small percentage of tin to azirconium uranium alloy. Other tests which were made, for example, on a5% uranium, 3% tin and 92% zirconium alloy showed the corrosion rateupon four weeks exposure to be only .20 milligram. Another samplecontaining as much as 20% uranium, 5% tin and zirconium showed a rate ofonly .63 after a two week run. It was, however, found that when an alloyhad a uranium content as high as 40%, the balance being 5% tin and 55%zirconium, it began to fall apart and appeared to be a dark grey powderafter a two week corrosion test, the sample losing some 10.68 milligramsper centimeter square per month. This is a marked indication that theeffect of tin for retarding the corrosion of uranium zirconium alloysstarts to fall off before a uranium content of 40% is reached.

The following tabulated data shows the effect of increasing the tinconcentration in a 20% uranium alloy with the balance Zirconium.

The following tabulated data was obtained with a 10% uranium alloy whenthe percent of tin was varied from to 5% 1 D.T-Discontinued test.

In view of its high corrosion resistance this alloy might in some casesbe used in the unclad condition in a nuclear reactor. However, in allprobability it will in most instances still be clad with either azirconium or aluminum or stainless steel cladding material, with thecorrosion resistance of the alloy being used somewhat in the form of aninsurance factor.

While the above description submitted herewith discloses a preferred andpractical embodiment of the corrosion resistant alloy of this inventionit will be understood that the specific details of construction andarrangement of parts described are by way of illustration and are not tobe construed as limiting the scope of the invention.

What is claimed is:

1. A corrosion resistant alloy of uranium, zirconium and tin whichcontains from about 1 to 30% uranium, from about 1 to tin and thebalance zirconium by weight.

2. A corrosion resistant alloy of uranium, tin and zirconium whichcontains from about 1 to 30% uranium, from about 1 to 5% tin and thebalance zirconium by weight.

3. A corrosion resistant alloy of uranium, zirconium and tin whichcontains approximately 20% uranium, 5% tin and the balance zirconium.

4. A corrosion resistant alloy of uranium, zirconium and tin whichcontains approximately 10% uranium, 5% tin and the balance zirconium.

5. A clad uranium containing body for a nuclear reactor, the core ofwhich consists essentially of a corrosion resistant alloy of uranium,zirconium and tin which contains from about 1 to 30% uranium, from about1 to 10% tin and the balance zirconium by weight, and having a metalcladding.

6. A clad uranium containing body for a nuclear reactor, the bodyconsisting of a corrosion resistant alloy of uranium, tin and zirconiumwhich contains from about 1 to 30% uranium, from about 1 to 5% tin andthe balance zirconium by weight and the cladding consisting essentiallyof a corrosion resistant metal.

7. A clad uranium containing body for a nuclear reactor, the core ofwhich consists essentially of a corrosion resistant alloy of uranium,zironium and tin containing approximately 20% uranium, 5% tin and thebalance zirconium, and having a metal cladding.

8. A clad uranium containing body for a nuclear reactor, the core ofwhich consists essentially of a corrosion resistant alloy of uranium,Zirconium and tin containing approximately 10% uranium, approximately 5%tin and the balance zirconium, and having a metal cladding.

No references cited.

1. A CORROSION RESISTANT ALLOY OF URANIUM, ZIRCONIUM AND TIN WHICHCONTAINS FROM ABOUT 1 TO 30% URANIUM, FROM ABOUT 1 TO 10% TIN AND THEBALANCE ZIRCONIUM BY WEIGHT.
 5. A CLAD URANIUM CONTAINING BODY FOR ANUCLEAR REACTOR, THE CORE OF WHICH CONSISTS ESSENTIALLY OF A CORROSIONRESISTANT ALLOY OF URANIUN, ZIRCONIUM AND TIN WHICH CONTAINS FROM ABOUT1 TO 30% URANIUM, FROM ABOUT 1 TO 10% TIN AND THE BALANCE ZIRCONIUM BYWEIGHT, AND HAVING A METAL CLADDING.